Chrome has entries in navigator.plugins for both application/pdf application/x-google-chrome-pdf, but the latter can't actually be used for an embed:  issue 531287 .

We've received a report from the Edge team of a site (honda.it) using the latter for PDF feature detection instead of the former.  Edge has only an try for application/pdf and it would be a shame if they had to add a fake x-google-chrome-pdf entry just for web compat reasons.

I propose we just remove our x-google-chrome-pdf entry as a bug-fix.  Since it's an internal mime-type it seems like a bug to me that it's web exposed at all.